Why does oxygen (O) not have a subscript/number?

1 Answer
Sep 13, 2016


Because we distinguish betrween oxygen, the atom, and oxygen, the element.


Elemental oxygen is a diatomic molecule, and we represent it as #O_2#, or as dioxygen. This is a different species from atomic oxygen, #O#, and we have to put in energy to make the transition to this species:

#O_2(g) + Delta rarr 2O(g)#